Had a little fender bender. Right after that i noticed the battery red light was on. When i got it home i took the solenoid off the firewall (all the battery wires meet here). When you put 12 volts to the small terminal, the solenoid pulls in and the two big terminals are connected together. That works. When installed on the truck and startup, i have no 12v voltage at the small terminal. Dont have a diagram, but service manual says something about fuse #14 under the dash feeding the "battery cutout".. Checked that fuse and its o.k. .... where does the 12 v signal to the solenoid come from ? I assume somehow it triggers after the alternator starts charging ?

 

It comes from the ignition switch through the neutral safety switch to the solenoid (relay) on the fender.

 

In FORD speak, that piece on the firewall is refered to as a "starter relay".

And not ALL the battery wires (cables) meet there. There is a battery cable that also runs from the battery directly to the starter motor.

One of those battery cables from the starter relay also runs down to the starter motor to control the starter solenoid on the starter motor.

It comes from the 40A fuse #111 in the BJB (Battery Junction Box) to the ignition switch.

With the key in the "start" position, the current then flows to the #18 15A fuse in the CJB (Central Junction Box, aka under the dash).

From fuse #18, if you have ESOF it goes to DTR (Digital Transmission Range) sensor, or if you have MSOF it goes to the CPP (Clutch Pedal Position) sensor (which has a jumper wire around the CPP sensor if automatic transmission).

From the DTR it goes to control the starter motor relay on the firewall.

It should "trigger" when you turn the ignition switch to the "start" position, at which time the alternator wouldn't have started charging yet. When the alternator begins to charge, the stator circuit feeds back a voltage through the regulator to the charge indicator light, causing it to turn off.

 

When the alternator output comes up, the regulator 'removes' ground from the charge lamp circuit putting it out as the indicator the alternator is functioning.
Check alternator output first before takeing things apart.
It may be the plug on the alternator, the regulator or the alternator proper.
The fuse feeding power through the ignition switch to the lamp obviously is not blown if it lights the lamp and there is a ground present from some source.
Either a lead is grounded, or it's comeing from the regulator.
Good luck.

 

I don't see how the firewall relay would effect charging. It just sends the trigger to the solenoid on the starter. Once that solenoid is pulled in and goes closed, it completes the 12 volts in that 4 gauge wire that runs down directly from the battery.....and the starter cranks. Where was the damage on the truck?

 

Tree ran into the front fender on passenger side. BAttery moved 6 inches. poked a small hole in the side. I put RTV over the hole, filled battery with water and charged up. Fixed tie rod and ball joint and started truck... BAttery light on. I measured voltage at the relay and dont have more than 12 volts on the battery or alternator lugs. Guess i wont help much to have the relay engage as the one terminal has no voltage anyway... Dont know if the "no alternator output" and "no signal to pull in relay" are related or not.. Ran out of time today to do any more tests. I did wiggle the cables on alternator and they seem to be connected. Have started truck a dozen times this week and runs / starts o.k.... just dont charge.

 

If it starts then that relay must be fine. I don't know what you mean by an altenator lug on that relay. My understanding is it has 3 lugs. One lug gets a trigger from the ignition circuit to close the relay. Another lug has 12+ from the main fuse that transfers that current to the 3rd lug which in turns is the trigger for the solenoid....I believe that is all it does. When it's running and you put a meter on the battery terminals, does it show 13.5 to 14 volts....somewhere in that area? If it reads 11-maybe..11.5 I would pull the altenator. Maybe you shorted it out when the battery got that hole poked in it or something grounded to positve for a time...dunno???? If it is charging and the light is still on....I have no clue.

 

battery side of the relay is 11.7 volt. Small signal terminal is 0 volts. Large output side of the relay is 0 volts..

 

Is that running or off?

 

both........

 

That's low, running or not.

That's good, weather running or not.

That's good, weather running or not.

So it appears to not be charging, like the alt light says.

Could you restate the problem?

And why do you think there is a problem with the starter circuit?

 

Is this on your 01 Screw ? I think you are on the wrong track looking at the start relay . Ck power supply to alt. If this happend after the crash ,ck the max fuse to the alt. and the wiring to it . I think the alt pwr wire goes to the junction panle at the pass firewall . Trace the big alt wire to it's end , there should be a max fuse or " fuse link " between the alt and the bat. Just a thought !

 

It may be the plug on the alternator, the regulator or the alternator proper.